I see.

Well basically he's going to spank you unless you drop a few grand. The GSX is a little faster stock, and can see much larger benefits from relatively minor modifications compared to a GSR. You have to spend like $800 just on i/h/e to put 155 hp to the wheels and run a 14.8 after a good launch.

If you're set on beating a GSX, a GSR is not a great choice.

If you want the GSR because you like the overall experience more than a GSX despite the lower power, go for it. Otherwise if you are simply looking for bragging rights at low cost I would suggest a different car.